This application relates to a method and a device for displaying stereoscopic video images. Such methods are known and are associated in practice with a certain outlay in order to ensure that the stereo images displayed are also of satisfactory quality and, chiefly, also to ensure that the right and left frames are displayed in the correct sequence.
In order in conjunction with good resolution to permit an essentially flicker-free display, an American Patent Specification U.S. Pat. No. 5,083,851 proposes to present within 30 ms under computer control for each eye of a viewer two different fields (an even one and an odd one) each. The resolution is substantially improved thereby, the more so as each eye is fed--at least in theory--the complete image information of the respective frame. For this purpose, the method uses a frame store which stores as a whole all four fields of two frames during 60 ms and outputs them twice (during 30 ms in each case) to the display. This known method is represented in FIG. 3 as the prior art.
According to the known method, during 15 ms the left eye is presented with a left even field, and the right eye is presented with a right odd field, whereas in the next 15 ms the left eye is presented with a left odd field and the right eye is presented with a right even field. This process is then repeated once during the next 30 ms before then a new left and a new right frame are read into the frame store. A shutter opens the view onto the display for the left and right eyes alternately, so that during 60 ms the shutter must change its state eight times in order to make the respective frames accessible to the respective eyes. This means a relatively high operating frequency and corresponding quality requirements of the shutter, which is mostly designed as an LCD switching element and is therefore more difficult to operate with increasing operating frequency, since the inertia of the liquid crystal elements has a braking effect. In the case of slight operating delays, crosstalk can easily occur, in which case one eye disadvantageously is also fed field information or parts thereof which are intended for the other eye, and the resolution, which is good per se, could again be ruined. The persistence of a monitor, for example, has a certain significance in this case. In this known method, it is permitted to be only extremely short (at most approximately 4 ms), since an eye requires a field with preferably black image information per displayed field. However, if such a field still persists with its previous picture content, this is as a rule a picture content which is intended only for the other eye. However, since this picture content is on one field whereas the picture content to be correctly displayed is on the other field, it will not be successively overwritten, but possibly not until after 8 ms when the lines of this field are overwritten again. This can lead to discomfort for the viewer. In order to keep this as slight as possible, the persistence of the screen must be reduced, and this can lead to an objective light loss which is precisely extremely undesirable in sensitive applications such as, for example, in operation microscopy.
The more recent DE-C-4 134033 attempts, in the case of a similar method, which in particular aims to manage with conventional video cameras and conventional television sets, to prevent the disadvantages mentioned by dispensing altogether with the display of an even and an odd field per frame and only at all displaying either an even or an odd field per frame. However, the method described there is unsatisfactory for increased demands on the display quality, since the resolution on the television set is unsatisfactory for such demands, all the more so since the entire display is carried out using field technology. In this technology, one field per frame is essentially dispensed with, with the result that for one eye of a viewer respectively only one field (for example, the even one) of a frame (for example, the right one) is displayed, while for the other eye respectively only another field (for example, the odd one) of another frame (for example, the left one) is displayed.
The resolution of the stereoscopic image on the television screen is thus unsatisfactory for many applications in the case of known methods, the shutter frequency is undesirably high in the case of the method first described, the screen brightness is unsatisfactory in the case of some known solutions, and the risk of crosstalk is not completely removed, which can lead in the case of lengthy viewing to headache and discomfort.